Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they do have a number of limitations, present risks to the patient, are invasive and uncomfortable for the patient, and their cost restricts their application as routine health-screening tools.
Because of the difficulty traversing a convoluted passage, endoscopes cannot reach the majority of the small intestine and special techniques and precautions, that add cost, are required to reach the entirety of the colon. Endoscopic risks include the possible perforation of the bodily organs traversed and complications arising from anesthesia. Moreover, a trade-off must be made between patient pain during the procedure and the health risks and post-procedural down time associated with anesthesia. Endoscopies are necessarily inpatient services that involve a significant amount of time from clinicians and thus are costly.
An alternative in vivo image sensor that addresses many of these problems is capsule endoscope. A camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An autonomous capsule camera system with on-board data storage was disclosed in the U.S. patent application Ser. No. 11/533,304, entitled “In Vivo Autonomous Camera with On-Board Data Storage or Digital Wireless Transmission in Regulatory Approved Band,” filed on Sep. 19, 2006. This application describes a motion detection is conducted using a portion of each image, the portion being stored in a partial frame buffer. In one embodiment, two partial frame buffers are used as an operand buffers for a reduced version of a current image and a reference image, respectively. The reference frame buffer corresponds to the one containing a previously stored or transmitted digital image. When the image in the operand partial frame buffer is determined not to be stored, that partial frame buffer may be overwritten by the next digital image to be motion-detected. Otherwise, the operand partial frame buffer would be designated the next reference partial frame buffer, and the current reference partial frame buffer is designated the next operand partial frame buffers. In the above application, a metric for measuring the degree of motion between the two partial images described and is used to compare with a threshold as to whether to capture an underlying image or as to determine a proper compression ratio for the underlying image.
While the motion detection has greatly helped to eliminate some unnecessary image capture and conserved the precious on-board storage and battery power, it may not fully address dynamic environmental issue. The environment in the small intestine and that in the colon may present very different imaging environment. For example, the small intestine has a smaller average diameter than the colon. Therefore, the distance between the capsule camera and a non-contacting lumen wall being imaged is closer for the small intestine than the colon. Furthermore, the average transit time for the capsule camera to travel through the small bowel is about 5 hours while the average transit time to travel through the colon is about 30 hours. On the other hand, the length of the former is about 6 meters and the latter is about 1.5 meters. Therefore, the average transit speed in the small intestine is about 20-30 times faster than the transit speed in the colon. The average transit speed can also be used as an indication to differentiate the environment between the small intestine and the colon.
Furthermore, a combination of the distance between the camera and lumen walls and the average transit speed are useful information to differentiate the environment between inside the intestine and inside the colon. For a capsule camera intended to image the colon, it will be beneficial that the capsule camera is able to detect the environment change when the capsule camera enters the colon from the small intestine. Accordingly, the capsule camera may be operated in a very low power mode and/or a mode where the archive memory is not filled up as quickly as normal mode before it enters the colon. Therefore, it is desirable to develop systems and methods that provide environment change detection and configure the capsule camera accordingly depending on the environment. For a capsule camera intended for imaging the colon, the system may provide control signals required to configure the capsule camera to capture and store images with adequate quality and illuminating light when the detection of the environment change corresponding to entrance into the colon from the small intestine is asserted.